1. Field
The subject invention relates to plasma reactors and, especially to uniform gas distribution in inductively-coupled plasma reactors.
2. Related Art
Plasma reactors or chambers are well known in the art and are widely used in the fabrication of semiconductor integrated circuits, flat panel displays, light emitting diodes, solar cells, etc. In a plasma chamber it is conventional to apply RF power to ignite and sustain the plasma inside the vacuum chamber. There are various manners in which the RF power can be applied, and each design has different characteristics, e.g., efficiency, plasma dissociation, uniformity, etc. One technology that is relevant to this disclosure is inductively-coupled plasma (ICP) chambers.
In inductively-coupled plasma processing chambers, an antenna, usually in the form of a coil, is used to transmit the RF power into the chamber. In order to couple the RF power from the antenna into the chamber, a dielectric window is provided at the location where the antenna is situated. In chambers for processing substrates, such as, e.g., silicon wafers, the substrate is situated on a chuck and the plasma is generated above the substrate. Therefore, the antenna is positioned over the ceiling of the chamber, such that the ceiling is made of a dielectric material or includes a dielectric window.
In plasma processing chambers, various gasses are injected into the chamber so that chemical and/or physical interaction of ions with the substrate can be used to generate the various features on the substrate by, e.g., etch, deposition, etc. In many such processes, one parameter of high importance is within-wafer process uniformity. That is, a process that is occurring at the center of the substrate should be of identical or highly similar characteristics as the process occurring at the edge of the substrate. Thus, for example, when performing an etch process, the etch rate at the center of the wafer should be the same as that at the edge of the wafer.
One parameter that helps in achieving good process uniformity is even distribution of process gases within the chamber. To achieve such uniformity, many chamber designs employ a showerhead situated above the wafer to uniformly inject the process gasses. However, as noted above, in ICP chambers, the ceiling must include a window for the RF power transmitted by the antenna. Consequently, such design does not lend itself to showerhead implementation of gas injection.
FIG. 1 illustrates a cross-section of a prior art ICP chamber design. ICP chamber 100 has a generally cylindrical metallic sidewall 105 and a dielectric ceiling 107, forming a tight vacuum enclosure that is pumped by vacuum pump 125. A pedestal 110 supports a chuck 115, which holds the substrate 120 to be processed. RF power from RF power supplier 145 is applied to antenna 140, which is generally in the form of a coil. Processing gas is supplied from gas source 150 via pipelines 155 into the chamber to ignite and sustain plasma, and thereby process the substrate 120. In standard ICP chambers, the gas is supplied into the vacuum enclosure either by circumference injectors/nozzles 130, by central nozzle 135, or both.
As can be appreciated from FIG. 1, the gas from the circumference injectors 130 is largely pumped out and is not effectively dissociated to reach the wafer 120 surface. Thus, much of the gas from the circumference injectors 130 may be processed at the edge of the wafer, but little reaches the center of the wafer 120, leading to non-uniformity. Conversely, gas provided from the central nozzle 135 is concentrated at the center of the wafer and is not used at the edge of the wafer, also leading to non-uniformity.
Accordingly, there is a need in the art for an improved ICP chamber design that improves gas distribution within the chamber to provide enhanced process uniformity.